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Broken Spokes From Surface Rust

Fri, 05/01/2009 - 23:05 — Brent

When building your own wheels -- or anything -- ensuring you have quality parts is paramount. I've built many wheels now and usually use DT Swiss spokes, but for my custom trike project, the spoke vendor wasn't known. And it had disastrous results.

Last year my recumbent trike (link in progress) developed a case of Spokus Brokenus on one of its front wheels. It's a "tadpole" trike, which means there is one wheel in back for propulsion, and the two in front steer. It was odd that just the one front wheel had this issue, but it became clear why.

I normally parked the trike at the front of the garage, which happened to be the resting place of the lawn mower. The short of it is this: Mix low quality spokes with a mower's damp bits of grass, and you have a corrosive situation. The spokes would pop apart in my hand with the slightest increase in tension. I think in the end, nearly 1/3 of the spokes broke. Fortunately, not while I was riding.

Meanwhile, I used the same spokes on the other two wheels, and have had no problems, but those spokes are also rust free. It's interesting how the spokes were breaking. As soon as the surface rust developed, the corrosion would enter the spoke shaft, and slowly eat through the spoke. The spokes that popped sometimes had breaks in two or three other spots. Bending these spots open showed corrosion about 1/2 or 2/3 the way through the spoke. So for many spokes, very little material was holding the tension.

Here are two of these spokes. The top spoke broke in the wheel, and had the one additional kink pictured when I removed it from the hub. The bottom spoke wasn't broken in the wheel, but when I removed it and bent it, the spoke broke in three places.

A closeup of the top spoke shows the rust and a little more detail around the break. This spoke was in about the worst condition.

Since these wheels are a bit odd -- 20" BMX rims with downhill MTB hubs with a 20mm axle -- finding spokes in such an abbreviated length was difficult. However, I found a good supplier of DT Swiss, and rebuilt the wheels with black 2.0mm spokes, black brass nipples, and they look sharp.